AA5342 Down DCA

[Commando Cody]

Originally Posted by Lead Balloon

It appears from the NTSB's most recent press conference that the instruction "pass behind the CRJ" was not heard in the helo's CVR and, therefore by inference, not heard by the crew. Am I correct in assuming that there is no requirement to readback an instruction like that in the USA? ATC appeared not to expect one.

The Aeronautical Information Manual lists a number of instructions that should be read back, but there are none that must be read back (unless the controller specifically requests). "Pass behind..." is not even one of the "should" be read back instructions, so ATC wouldn't be bothered by not getting a read back. Frankly, if there was a requirement to fully read back all things like "Pass behind..." the frequency would be constantly full. In any case, whether PAT25 heard the "Pass behind" or not, it had already said that it was providing its own visual separation, so not hearing an instruction to pass behind does not take away the requirement to maintain separation.

[goeasy]

Didn’t NTSB say today that FDR had ‘data error’ instead of altitude indicating possibility of pitot/static problem? Said they were going to try rebuilding system to test it, which won’t be easy or quick!

[Wide Mouth Frog]

I think we're flogging a dead horse with this altitude thing, we already know that the aircraft collided from the video.

The most reliable information from the helicopter indicates they were at 278ft above the water. Likewise we're told that the CRJ was at 313ft 2 seconds before impact. The CRJ is 20ft tall, more with landing gear extended. The UH60 is 16ft tall. There is no more information to be gleaned from this.

The CRJ was a passenger jet on finals to land and there is no way on earth anything else should be on a collision track. The helicopter should never have been allowed to be that close to landing traffic, no matter what the legal and procedural niceties of ATC communication were.

And the fact that there were numerous reports of similar close calls of this kind over the previous decade or so is a damning (some might say criminal) indictment of the safety management systems of the authorities involved.

[ATC Watcher]

​​​​​​The helicopter should never have been allowed to be that close to landing traffic,

absolutely . the altimeter talk is just a distraction or at best contributing factor, Not the cause .. which brings us back to the safety assessment of the procedure , which the NTSB did not mention at all,, but I am sure , or at least I hope they will go into in their final report.
In any case the procedure us currently withdrawn until end of March and I sincerely doubt they will re-install it before the final report is out. ..

A couple of new info points the NTSB clarified : Both aircraft were on VHF , so we can drop this UHF discussion , the Blackhawk had ADS-B equipped but was not transmitting , it was check ride with NVG, and they most probably all had them on .and there was a last second evasive action attempt by the CRJ crew, which go a TA previously . On the TWR, the CAs are displayed in the BRITE even with audio on ..
For the rest we have to wait until the next NTSB briefing

[Someone Somewhere]

One could also argue that a CRJ overflying a helicopter by 50-100 ft is going to throw a pretty bad wake turbulence into the helicopter, and the helicopter losing control and crashing seems pretty likely. Save the CRJ, sure.

[dbcooper8]

The L model radar altimeter indicators each contain a pointer that indicates altitude on a linear scale from 0 to 200 feet (10 feet per unit) and a second-linear scale from 200 to 1500 feet (100 feet per unit). In other words 300 feet could easily be misread as 210 feet for the uninitiated. Worth noting the pointer is the width between 200 feet and 300 feet. Also, was the bug in use and if so what altitude was it set to?

Disconcerting that the PAT 25 crew, about to descend and fly less than 200 feet AGL , would not have investigate the discrepancy of 100 feet between their respective altimeters...

[Easy Street]

Originally Posted by ATC Watcher

absolutely . the altimeter talk is just a distraction or at best contributing factor, Not the cause .. which brings us back to the safety assessment of the procedure , which the NTSB did not mention at all,, but I am sure , or at least I hope they will go into in their final report.

+1 to everything you and Wide Mouth Frog said.

I sincerely hope the NTSB can avoid being distracted by the distractions of altimetry and the missing ATC words on the Blackhawk CVR.

Upthread, Luca Lion calculated the 3 degree PAPI approach path as crossing the eastern riverbank at 270ft. If that's correct, then the CRJ's 313ft radar height 2 seconds before collision puts it at least 43ft above the approach path, so the Blackhawk's radio height deviation of 78ft would have contributed only about 35ft to the erosion of any intended "procedural separation" (*) between the aircraft. Or, to put it another way, the same outcome would have resulted if the Blackhawk had been at 235ft radio and the CRJ on the glide. Height keeping of plus or minus 35ft can only be achieved by instrument flying, which is obviously not compatible with visual separation (or indeed VFR) so cannot be reasonably cited as part of a safety case for the procedure. And of course a landing aircraft could easily be below the glide. Altimetry and height keeping are not the cause of this accident.

Missing the word "circling" wouldn't have influenced the helo crew getting visual with the CRJ at the time of the trasnmission. At best, it would have given them an extra nudge that "runway 33" (which was audible) meant the CRJ would be taking an easterly flight path. Missing "pass behind" with only a few seconds to collision was irrelevant if, as seems likely, the helo crew did not see the CRJ at that point.

(*) The quotes around "procedural separation" are intended to convey a tone of disgust and sarcasm.

[Lead Balloon]

...
I was recently watching a video on the highlights of Oshkosh, the relevance of which will hopefully become clear shortly.

One part of the video was some POV footage from the cockpit of one of the Blue Angels. I had a 'double-take' and triple rewind to confirm what I thought I saw on the glareshield: I think I saw a piece of portable avionics that is very, very familiar to me.

Is any expert able to confirm what that white block on the glareshield is?

I've been in a discussion about the complexity of avionics upgrades to military flying machinery, the discussion precipitated by the differing terminology about "fitted with" and "equipped with" and "carried". And I suggest that even if the helo was "fitted with" an ADS system, at the altitude the aircraft were operating at the time of the collision any alerts may have been suppressed.

[Winterapfel]

Originally Posted by Easy Street

+1 to everything you and Wide Mouth Frog said.

I sincerely hope the NTSB can avoid being distracted by the distractions of altimetry and the missing ATC words on the Blackhawk CVR.

Upthread, Luca Lion calculated the 3 degree PAPI approach path as crossing the eastern riverbank at 270ft. If that's correct, then the CRJ's 313ft radar height 2 seconds before collision puts it at least 43ft above the approach path, so the Blackhawk's radio height deviation of 78ft would have contributed only about 35ft to the erosion of any intended "procedural separation" (*) between the aircraft. Or, to put it another way, the same outcome would have resulted if the Blackhawk had been at 235ft radio and the CRJ on the glide. Height keeping of plus or minus 35ft can only be achieved by instrument flying, which is obviously not compatible with visual separation (or indeed VFR) so cannot be reasonably cited as part of a safety case for the procedure. And of course a landing aircraft could easily be below the glide. Altimetry and height keeping are not the cause of this accident.

Missing the word "circling" wouldn't have influenced the helo crew getting visual with the CRJ at the time of the trasnmission. At best, it would have given them an extra nudge that "runway 33" (which was audible) meant the CRJ would be taking an easterly flight path. Missing "pass behind" with only a few seconds to collision was irrelevant if, as seems likely, the helo crew did not see the CRJ at that point.

(*) The quotes around "procedural separation" are intended to convey a tone of disgust and sarcasm.

Following "5*why", keep asking...
Why did the did miss part of the message
Why was the incomplete read back missed
Why does missing a few words lead to this disaster within seconds.

Does this lead an answer like: helicopter in a very busy airspace, busy controllers (insufficient time to be fully focused on full read backs) being by default too close to (and even needing to cross) the glideslope.
​​​​​​

[eglnyt]

Originally Posted by DIBO

that seems indeed to be the more professional terminology


And before people start jumping all over this 'feature', yes, yes, indeed an extra 'button' needs to be provided on the radio, to knowingly override the 'Tx Inhibit' feature in case of stuck mic., etc.

My former colleagues spent a lot of time running trials and writing a number of technical reports to evaluate the benefits and dis-benefits of TX inhibit for VHF AM as the purveyor of a proprietary solution in the early 90s lobbied anybody that would listen to try and sell their product. In the end it was concluded that the benefit was slight compared to the cost of installation and ongoing maintenance. The UK CAA declined to make it mandatory and as you know anything optional isn't likely to get bought if it has no cost benefit. One airline no longer in business did fit it to a number of their fleet but they are all long since scrapped and to be honest that airline was nowhere near top of the list for crew that didn't listen before pressing the button and unless you protect against the main culprits you aren't achieving anything. Any "extra" button is a killer to any idea in an airliner flight deck but that device used a double key as the override to get around that.

In the case in hand if the step on was from the helicopter then they were stepping on a transmission addressed to them which, regardless of the effect of the overstepped information they didn't receive, might indicate that communication with the Tower adjacent to a very busy airfield was not as high a priority as perhaps it should have been.

For proper radio and full duplex, the kind we all take for granted with the devices in our pockets, you probably need to wait for the digital revolution in civil aviation. The cost for poorer countries, and more significantly the large military fleets tied into expensive and slow upgrade programmes, means you will probably wait a long time.

[Easy Street]

Originally Posted by Winterapfel

Following "5*why", keep asking...
Why did the did miss part of the message
Why was the incomplete read back missed
Why does missing a few words lead to this disaster within seconds.

Does this lead an answer like: helicopter in a very busy airspace, busy controllers (insufficient time to be fully focused on full read backs) being by default too close to (and even needing to cross) the glideslope.
​​​​​​

I hadn't intended to go all the way along the causal chain in my post. But since you ask, I think your answer only goes one step further. There are more steps to take.

Helicopters in busy airspace are not a problem if a safe system exists for separating them from airline traffic.

There is no evidence yet of the controller having made a mistake. He was undoubtedly busy, but that was not his fault. What could be done about it? The answers to that question take us another step along the causal chain:

1. The FAA could have provided more controllers. We know the helicopter controller position was unoccupied, and it's likely that closer monitoring and earlier intervention could have changed the outcome (notwithstanding point 3).
2. Controller workload could have been reduced by implementing effective procedural separation. If the DCA ATC rulebook allowed this segment of Route 4 to be in simultaneous use with Runway 33 landings, then procedural separation did not exist, however much anyone thought it did. At least 1.5nm or 500ft between flight paths would be needed to meet the least restrictive FAA separation standards, and this would have forced constraints to be applied to Route 4 or Runway 33 utilisation.
3. Regulations allowed the helo pilots to assume responsibility for separation. This is what happened, with the consequences which flow from the inherent difficulty of identifying and separating visually at night (especially while wearing NVG).

The authorities (by which I mean FAA and DoD) have questions to answer on all three points. Why was the helicopter controller position vacant? Did the ATC rulebook or staffing requirements rely on a false assumption that procedural separation existed? How did any such assumption remain in place after previous near misses? Is visual separation between helicopters and airline traffic a reasonable thing for regulations to permit, at night and using NVG? Ultimately it seems to have routinely been used as a release valve for the pressure building in the system due to the failure to address points 1 and 2.

Hopefully the investigation will be bold enough to ask these questions, which expand the potential scope of responsibility well beyond the individual controller and pilots.

[Chock Puller]

Lead Balloon's posted video.......

You Tube

[island_airphoto]

Originally Posted by Chock Puller

Lead Balloon's posted video.......

https://www.youtube.com/watch?v=nr745tCMeKI

Is that Stratux or similar ADS-B receiver?

[ATC Watcher]

Originally Posted by island_airphoto

Is that Stratux or similar ADS-B receiver?

looks like the new Stratus 3 .. Nice piece of kit.

https://www.youtube.com/watch?v=OEgPVCTsBeU&t=5s

[RatherBeFlying]

I believe radalts are configured to display height above gear; so add ≈16' height of Blackhawk to 278' yielding 294'. Then there's rotor bowing, and how much higher will the tail rotor arc be at the speed the helo was flying?

Likely the Kollsman settings will be recoverable. Barometric altimeters used in VFR can be way off, but transponder calibration depends on a calibrated altimeter. The NTSB will be looking at maintenance records.

[MPN11]

Whilst these are valid observations, it is also micro-managing a procedure whose altitude separation was always totally flawed. I cannot personally attribute any blame to ATC or either pilot when the scenario was so badly devised ... and that means not only the infamous Route 4 but the concept of visual separation in the dark.

It was doomed to fail, eventually, but sadly someone [other than those directly impacted] never saw it coming. THEY are the culprits.

MPN11, former Mil ATCO

[island_airphoto]

Originally Posted by MPN11

Whilst these are valid observations, it is also micro-managing a procedure whose altitude separation was always totally flawed. I cannot personally attribute any blame to ATC or either pilot when the scenario was so badly devised ... and that means not only the infamous Route 4 but the concept of visual separation in the dark.

It was doomed to fail, eventually, but sadly someone [other than those directly impacted] never saw it coming. THEY are the culprits.

MPN11, former Mil ATCO

Pretty much it, everyone had to be lucky every time, gravity only had to be lucky once. The altimeter issues are a red herring at best, the helicopter crew were not trying to go directly under the airplane.

[Stagformation]

Originally Posted by dbcooper8

The L model radar altimeter indicators each contain a pointer that indicates altitude on a linear scale from 0 to 200 feet (10 feet per unit) and a second-linear scale from 200 to 1500 feet (100 feet per unit). In other words 300 feet could easily be misread as 210 feet for the uninitiated. Worth noting the pointer is the width between 200 feet and 300 feet. Also, was the bug in use and if so what altitude was it set to?

Disconcerting that the PAT 25 crew, about to descend and fly less than 200 feet AGL , would not have investigate the discrepancy of 100 feet between their respective altimeters...

Details of instrumentation here:
https://apps.dtic.mil/sti/tr/pdf/ADA409934.pdf
Not completely obvious in the photo is the digital display of radar altitude just underneath the annotation ABS ALT. The technical manual also mentions a three digit radar altitude displayed on the HUD.

[Lead Balloon]

As someone with an insight into the complexities of retrofitting certified avionics hardware and the associated wiring, controllers and antennae to fighter jets and other military aircraft, I would be completely unsurprised if, as seems to be evident from the video imbedded at #1112, the USA’s elite, pre-eminent military aerobatics team uses a portable ADS-B unit velcro’ed to the aircraft’s glare shield. And if it’s OK for them, I can’t see why it wouldn’t be OK for the PAT helicopters and I wouldn’t be surprised if that’s the ADS-B to which various references having been made.

I suppose the operational question is whether the aircraft on which these portable units are used are permitted to fly without them on board and working. My guess is that there will be no prohibition. They are just ‘nice to haves’ but not essential for the ops in which they engage.

And there’s a causal question anyway: Would a functioning ADS-B system – portable or otherwise - on the PAT helo have made any difference? The answer depends on the variables around the alert suppression parameters in each aircraft’s systems and the effectiveness of the format of alerts – if any – given in each cockpit.

[island_airphoto]

Originally Posted by Lead Balloon

As someone with an insight into the complexities of retrofitting certified avionics hardware and the associated wiring, controllers and antennae to fighter jets and other military aircraft, I would be completely unsurprised if, as seems to be evident from the video imbedded at #1112, the USA’s elite, pre-eminent military aerobatics team uses a portable ADS-B unit velcro’ed to the aircraft’s glare shield. And if it’s OK for them, I can’t see why it wouldn’t be OK for the PAT helicopters and I wouldn’t be surprised if that’s the ADS-B to which various references having been made.

I suppose the operational question is whether the aircraft on which these portable units are used are permitted to fly without them on board and working. My guess is that there will be no prohibition. They are just ‘nice to haves’ but not essential for the ops in which they engage.

And there’s a causal question anyway: Would a functioning ADS-B system – portable or otherwise - on the PAT helo have made any difference? The answer depends on the variables around the alert suppression parameters in each aircraft’s systems and the effectiveness of the format of alerts – if any – given in each cockpit.

For us lowly civilians a Velcro ADS-B receiver isn't getting you within 30 miles of KDCA, you need it to transmit too. The helicopter having even receive ADS-B would have helped hugely if they looked at it, the fact they weren't looking at the plane they thought they were would have been pretty apparent.